The population of the elderly is increasing worldwide. Due to better dental health care, the elderly are retaining their teeth longer. Receding gum line with age results in exposed root dentin that becomes susceptible to dentin hypersensitivity (DH) and root caries formation—two major concerns in oral health. (Keltjens, et al., Int Dent J (1993) 43: 143-148; Percival, et al., J Med Microbiol (1991) 35: 5-11) In addition, DH is experienced by as high as 57% of young and old population (Drisko, et al., Int Dent J (2002) 52: 385-393) with exposed dentin that may have been caused by erosion (e.g., due to external acids from food or drink), abrasion (due to excessive or improper tooth brushing), aging (gum recession), or periodontal treatment.
The accepted definition of dentin hypersensitivity (DH) is that “it is characterized by short sharp pain arising from exposed dentin in response to stimuli, typically thermal, evaporative, tactile, osmotic or chemical and which cannot be ascribed to any other form of dental defect or pathology”. (Holland, et al., J Clin Periodontol (1997) 24: 808-813) The hydrodynamic mechanism for DH first proposed by Gysi and expanded by Brannstrlm et al in 1972 and Pashley in 1990, stated that an stimulus applied to exposed dentin cause an increase in the rate of fluid flow in the dentinal tubules “causing a hydrodynamic pressure change across dentin, activating the pulpal nerve fibers and evoking pain”. (Gysi, Br J Dent Sci (1900) 43: 865-868, Brannstrom, et al., Int Dent J (1972) 22: 219-227; Pashley, Dent Clin North Am (1990); 34: 449-473; Addy, et al., J Clin Dent (2010); 21[Spec Iss]: 25-30) The intensity of dentin hypersensitivity has been associated with the number and width of exposed tubules. (Pashley, et al., Arch Oral Biol (1985); 30: 731-737) Strategies to treat dentin hypersensitivity have included chemical or physical means of blocking or modifying pulpal nerve response to external stimuli, and/or occluding dentinal tubules to stop or reduce the fluid flow across dentin. (Addy, et al., J Clin Dent (2010); 21 [Spec Iss]: 25-30) Desensitizing agents to block pulpal nerve response include treatments with potassium and stannous salts or the more recently introduced arginine-containing desensitizing agent. (Markowitz, J Clin Dent (2009); 20 (spec Iss); Wolff, Adv Dent Res (2009); 21: 21-24) Agents that occlude dentinal tubules by forming precipitates have included: use of strontium chloride and sodium fluoride, potassium nitrate and potassium oxalate, dentin bonding agents. (Kishore, et al., J Endod (2002); 28: 34-35; Gillam, et al. J Oral Rehabil (2001); 28: 1037-1044; Trowbridge, et al., Dent Clin North Am (1990); 34: 561-581)
It would be desirable to provide a treatment in modifying the dentin surface by promoting occlusion of dentinal tubules and increasing the resistance of the dentin surface and the dentin tubule precipitates to acid dissolution. Since dentin tubule occlusion is associated with dentin hypersensitivity, such a treatment may have the potential of minimizing dentin hypersensitivity by occluding dentin tubules with precipitates that are less susceptible to acid dissolution.
Enamel and dentin caries are initiated by the dissolution or demineralization of the enamel or dentin mineral by acids produced by oral bacteria. In the case of dentin caries, the fermentation of the food carbohydrates by the oral bacteria produces acid that initiates the caries process, i.e., dissolution of the dentin mineral followed by the breaking down of the organic matrix (primarily, collagen) by the bacterial enzymes (Featherstone, Am J Dent (1994) 7(5):271-4; Zambon, et al, Am J Dent (1995) 8(6):323-8).
Earlier culture-based (Bowden, et al., Oral Microbiol Immunol (1990) 5(6):346-51; Ellen, et al., J Dent Res (1985) 64(10):1245-9) and more recent culture-independent studies (Chhour, et al., J Clin Microbiol (2005) 43(2):843-9; Preza, et al., J Clin Microbiol (2008) 46(6):2015-21) have shown that Streptococcus mutans and lactobacilli are the principal microorganisms associated with root caries.
Root caries has become a significant oral health issue. Periodontal disease or its treatment leads to gingival recession resulting in the exposure of the root surfaces supragingivally (Katz, et al., Caries Res (1982) 16(3):265-71; Ravald, et al., J Clin Periodontol (1986) 13(8):758-67) that become susceptible to caries development. According to epidemiologic studies, root caries especially among the middle aged and the elderly, is prevalent among patients with treated and untreated periodontal disease.
Current therapies to prevent or arrest dentin or root caries through remineralization process include: mouth rinses (Schlueter, et al., Arch Oral Biol (2009) 54(5):432-6), fluoridated dentifrices (Ganss, et al., Caries Res (2004) 38(6):561-6), varnishes (Beltran-Aguilar, et al., J Am Dent Assoc (2000) 131(5):589-96) and gels (van Rijkom, et al., Caries Res (1998) 32(2):83-92) and calcium phosphate remineralizing solutions. (Reynolds, J Dent Res (1997) 76(9):1587-95).
The presence of fluoride (F−) ions increases the mineralizing efficiency of the CaP solutions and inhibits enamel dissolution by the formation of less soluble fluoridated hydroxyapatite (LeGeros, J Dent Res 69 Spec (1990) No (567-74; discussion 634-6; LeGeros, J Clin Dent (1999) X(2):65-73; Moreno, Int Dent J (1993) 43(1 Suppl 1):71-80). In addition, F− ions reduce the metabolism of oral bacteria. (Van Loveren, et al., J Dent Res (1987) 66(11):1658-62C) Prevention of the adherence of cariogenic bacteria to tooth surfaces is considered to be an important strategy for controlling dental caries (Marsh, BMC Oral Health (2006) 6 Suppl. 1 (S14)). It was reported that a barrier-like film layer plays an important role in protecting dentin from physical, chemical and biological stimuli (Tagami, et al., Japanese Adhesive Dentistry, (1999) 17(56-60)). All-in-one adhesives (a fluoride-releasing adhesive) coated on the root dentin can inhibit Streptococcus mutans biofilm formation through a protective layer covering exposed root dentinal surfaces. (Daneshmehr, et al., J Dent (2008) 36(1): 33-41)
Because root caries is a plaque-related disease associated with specific microorganisms (Beighton, et al., J Dent Res (1993) 72(3):623-9), mineralizing agents combined with mechanical and/or chemical treatments to control bacterial plaque are necessary for preventing and arresting root caries (Petersson, et al., Gerodontology (2004) 21(2):85-92).
Zinc (Zn2+) ions released from zinc salts have been shown to provide antibacterial property, inhibiting plaque formation and gingival inflammation (Eisenberg, et al., Caries Res (1991) 25(3):185-90; (Sanz, et al., J Clin Periodontol (1994) 21(6):431-7). Our previous studies showed that polymer membranes (such as those used for guided bone regeneration) when mineralized with zinc-containing calcium phosphate compound, inhibited the growth and colonization of oral bacteria (Chou, et al., Implant Dent (2007) 16(1):89-100). Another study demonstrated that Zn-releasing calcium phosphate compounds deposited on orthodontic brackets also inhibited in vitro bacterial growth and development (Park, et al., J Dent Res (2005) 84 (1917). It would be beneficial to provide solutions for increasing resistance to acid dissolution and in inhibiting the adherence and colonization of cariogenic organisms such as Streptococcus mutans on dentin surfaces.